Rotor Cap Removing Tools, Microwave Guides, and Methods

ABSTRACT

Apparatuses and methods for removing caps, such as NMR rotor caps. The apparatuses and methods may permit caps to be removed in a manner that minimizes damage to equipment and instruments. Microwave waveguides that may include an elongated waveguide, a spline horn, and a slotted waveguide. Analytical instruments that include the waveguides.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 17/104,057, filed Nov. 25, 2020, now U.S. Pat. No. 11,703,555,which claims priority to U.S. Provisional Patent Application No.62/939,766, filed Nov. 25, 2019. The content of these applications isincorporated by reference herein.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT

This invention was made with government support under contractsDMR-1644779, DMR-1157490, and CHE-1229170, awarded by the NationalScience Foundation. The government has certain rights in the invention.

BACKGROUND

Nuclear magnetic resonance (NMR) rotors may be used to hold samplesduring a number of tests, such as magic angle spinning NMR experiments.NMR rotors usually are small cylindrical cups with thin walls, typicallymade of hard ceramics. After filling a cup with a sample, a cap can beadded to close the cup before NMR experiments take place. The capstypically are made of plastic, and are pressed for a tight seal with acup.

When an experiment is finished, the sample may be removed from therotor. The first step is usually very delicate, and includes removingthe cap without damaging the cap and/or rotor. The cap is designed tostick out of the rotor, and a manufacturer or designer of the rotors andcaps usually provide a tool which can grab the cap.

The normal operation is to hold the rotor from one side and pull fromthe other side using the cap-grabbing tool. If this operation is notperformed in a straight fashion, damage usually occurs. For example, thecap can crack the rotor. Sometimes the crack is of such a small sizethat it is not visible to the naked eye. In such cases, the rotor cancrash in the NMR probe during operation, which may cause significantdamage, such as damaging the stator, and the sample and rotor usuallyare lost as well.

Such crashes can be extremely expensive (e.g., stators can cost tens ofthousands of dollars, some samples can take week or months forscientists to make, etc.).

Therefore, there remains a need for improved apparatuses for removingthe caps, including apparatuses that ensure cap removal is consistentlyperformed in a straight manner.

To perform dynamic nuclear polarization, one needs a NMR spectrometer incombination with a microwave source and microwave guiding system toirradiate the sample under study during NMR experiments. In particular,maintaining low loss microwave transport inside the NMR probe can bedifficult due to space, sample size, sample holder design limitation, ora combination thereof. The traditional approach has been to usecorrugated waveguides and launch the microwave beam from a distance ontothe sample holder.

Specifically, dynamic nuclear polarization probes typically use acorrugated waveguide and free space launch (sometimes in combinationwith a lens). Such apparatuses usually are complex, difficult tomanufacture, and/or the launching of the microwave onto the sample understudy is very inefficient, which may cause a high amount of microwavepower loss. In fact, current technology can be so complex thatmanufacturing certain parts can take 6 to 8 weeks of processing, requirethe use of sacrificial parts, and be very expensive. Contributing to theexpense is the high failure rate during manufacturing. Due to the highfailure rate, several parts usually need to be fabricated in order toobtain one acceptable part.

There remains a need for improved microwave transport efficiency, andapparatuses that are low loss, are simple to manufacture, have a lowercost of manufacture, use less material during manufacturing, or acombination thereof.

BRIEF SUMMARY

Provided herein are apparatuses and methods that address one or more ofthe foregoing disadvantages. For example, improved apparatuses andmethods are provided for removing caps, such as caps of NMR rotors,including apparatuses and methods that ensure cap removal isconsistently performed in a straight manner that eliminates or reducesthe risk of damage to one or more components and/or instruments.

Also provided herein are electromagnetic radiation wave guides,including a smooth wall microwave guide with extremely low loss that maybe small enough to fit inside an NMR probe. In some embodiments, thesmooth wall microwave guides are not corrugated, and, therefore, can besimpler to manufacture. In some embodiments, the microwave guidesprovided herein allow the guiding of microwaves inside a dynamic nuclearpolarization probe with minimal or reduced losses. The guides may allowsubstantially lossless microwave transmission, and/or are easier (and,therefore, less expensive) to manufacture than current technology.

In one aspect, apparatuses that may be used for removing a cap, such asa cap from an NMR rotor, are provided. In some embodiments, theapparatuses include a plate having a first side and a second side,wherein the plate includes a material defining a first aperture of thefirst side of the plate; a tightening screw configured to reduce orexpand a cross-sectional area of the first aperture; and at least onepushing screw arranged in at least one second aperture defined by thematerial, wherein each of the at least one pushing screws includes (i) afirst end extending from the second side of the plate, and (ii) a secondend that is extendible from the first side of the plate upon turning thefirst end.

In another aspect, methods for removing a cap, such as a cap from an NMRrotor, are provided. In some embodiments, the methods include providinga cap-removing apparatus as described herein; arranging at least aportion of an NMR rotor cap at least partially in the first aperture;turning the tightening screw to reduce the cross-sectional area of thefirst aperture to secure the NMR rotor cap in the first aperture; andturning the first end of the at least one pushing screw to extend thesecond end of the at least one pushing screw from the first side of theplate to apply a force to the NMR rotor with the second end of the atleast one pushing screw, wherein the force is effective to separate theNMR rotor cap from the NMR rotor.

In a further aspect, slotted waveguides are provided. In someembodiments, the slotted waveguides include a metallic tube having afirst end and a second end, wherein the metallic tube defines aplurality of slots in a surface of the metallic tube, and wherein thefirst end of the metallic tube is configured to be coupled to a devicefor directing or controlling electromagnetic radiation, such asmicrowaves. The second end of a slotted waveguide may be configured toreceive a sample tube, such as a sample tube formed at least in part ofa dielectric material. Non-limiting examples of dielectric materialsinclude plastic, glass, ceramic, or a combination thereof. Thedielectric material may be “microwave transparent”, as described herein.

In a still further aspect, microwave guides are provided. In someembodiments, the microwave guides include a slotted waveguide asdescribed herein; a spline horn coupled to the first end of the slottedwaveguide; and an elongated waveguide coupled the spline horn, theelongated waveguide including a tube having a substantially smooth innersurface. The spline horn may be configured to focus a diameter of a beamof electromagnetic radiation, such as a microwave beam, from theelongated waveguide down to an internal diameter of the slottedwaveguide.

In yet another aspect, analytical apparatuses are provided that includea slotted waveguide or microwave guide as described herein.

Additional aspects will be set forth in part in the description whichfollows, and in part will be obvious from the description, or may belearned by practice of the aspects described herein. The advantagesdescribed herein may be realized and attained by means of the elementsand combinations particularly pointed out in the appended claims. It isto be understood that both the foregoing general description and thefollowing detailed description are exemplary and explanatory only andare not restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A depicts a perspective view of an embodiment of a plate for anembodiment of a cap-removing apparatus.

FIG. 1B depicts a bottom view of an embodiment of a plate for anembodiment of a cap-removing apparatus.

FIG. 1C depicts a top view of an embodiment of a plate for an embodimentof a cap-removing apparatus.

FIG. 1D depicts a perspective view of an embodiment of a cap-removingapparatus.

FIG. 2 depicts an embodiment of a slotted waveguide.

FIG. 3 depicts an embodiment of a slotted waveguide, and an embodimentof a sample tube partially inserted into the slotted waveguide.

FIG. 4 depicts an embodiment of a microwave guide that may be used in ananalytical technique.

FIG. 5A depicts a top view of an embodiment of an adapter describedherein.

FIG. 5B depicts a cross-section of the embodiment of the adapterdepicted at FIG. 5A.

DETAILED DESCRIPTION

In one aspect, apparatuses and methods are provided that may be used toremove a cap, such as an NMR rotor cap. When the cap is an NMR rotorcap, the apparatuses and methods herein may permit the cap to be removedwithout damaging caps, rotors, and/or components of an instrument.

Cap-Removal Apparatuses and Methods

In some embodiments, the apparatuses provided herein include a platehaving a first side and a second side. The plate generally may have anyshape and size, including those explained herein.

In some embodiments, the plate is formed of a material defining a firstaperture of the first side of the plate. The “first aperture of thefirst side” includes an aperture that is accessible via the first sideof the plate. In some embodiments, the first aperture traverses theentire width of the plate, and, therefore, is accessible via the firstside and the second side of the plate. The first aperture generally mayhave any shape. In some embodiments, the first aperture is circular inshape, as depicted, for example, at FIG. 1A. The first aperture may haveany size that is effective to permit the receiving of a cap into thefirst aperture, and the tightening of the first aperture about the cap.In some embodiments, the first aperture may have a size effective toreceive and tighten about a cap, such as an NMR rotor cap, having adiameter of about 3 mm to about 5 mm.

The plate may be formed of any material. The material may include aflexible (e.g., a polymeric material) and/or malleable (e.g., a metal)material that permits a first aperture to be reversibly tightened asdescribed herein. In some embodiments, the material includes a metal. Insome embodiments, the material includes a polymeric material. In someembodiments, the material includes a metal and a polymeric material.

In some embodiments, the apparatuses include a tightening screwconfigured to reduce or expand a cross-sectional area of the firstaperture.

In some embodiments, the apparatuses include at least one pushing screwarranged in at least one second aperture defined by the material fromwhich a plate is formed. Each pushing screw may include (i) a first endextending from the second side of the plate, and (ii) a second end thatis extendible from the first side of the plate upon turning the firstend of the pushing screw. In some embodiments, the apparatuses feature1, 2, 3, 4, 5, or more pushing screws. In some embodiments, theapparatuses include two pushing screws, i.e., a first pushing screw anda second pushing screw.

An embodiment of an apparatus is depicted at FIGS. 1A-1D. FIG. 1Adepicts a perspective view of a plate, FIG. 1B depicts a bottom view ofthe plate, FIG. 1C depicts a top view of the plate 100, and FIG. 1Ddepicts a perspective view of the apparatus. The plate 100 of FIGS.1A-1D has a first side 101 and a second side 102. The plate defines anaperture 110 of the first side 101 of the plate 100. The plate 100 alsodefines an aperture 111 configured to accommodate a tightening screw(see FIG. 1D). The plate 100 also defines two apertures 120, each ofwhich is configured to accommodate a pushing screw (see FIG. 1D). Theplate 100 also defines an aperture 130 that can optionally accommodate ascrew or other fastener to permit the attachment of an accessory to theplate 100, such as a protective film (see FIG. 1D). FIG. 1D depicts aperspective view of an embodiment of an apparatus 150 that includes theplate 100 of FIGS. 1A-1C in which a tightening screw 160 is arranged inaperture 111, and a pushing screw 170 is arranged in each of the “secondapertures” 120. The embodiment of the apparatus 150 depicted at FIG. 1Dalso includes a screw 180 arranged in aperture 130. The screw 180secures a protective film 181 to the apparatus 150.

Although the plate of FIGS. 1A-1D has a first side that is circularshape (see FIG. 1B), other shapes are envisioned, such as square,rectangular, oval, etc. The plate, including its first side, generallymay have any dimensions. In some embodiments, the largest dimension ofthe plate (e.g., the diameter of the first side of a plate when thefirst side is circular) is about 0.75 inches to about 1.5 inches, orabout 0.9 inches to about 1.1 inches. Other dimensions, however, areenvisioned. Although the pushing screws depicted at FIGS. 1A-1D arethreaded screws, other configurations are envisioned, includingnon-threaded screws (e.g., bolts).

Also provided herein are methods for removing a cap. In someembodiments, the methods include providing a cap-removing apparatus asdescribed herein; arranging at least a portion of an NMR rotor cap atleast partially in the first aperture; turning the tightening screw toreduce the cross-sectional area of the first aperture to secure the NMRrotor cap in the first aperture; and turning the first end of the atleast one pushing screw to extend the second end of the at least onepushing screw from the first side of the plate to apply a force to theNMR rotor with the second end of the at least one pushing screw, whereinthe force is effective to separate the NMR rotor cap from the NMR rotor.

In some embodiments, the cap-grabbing apparatus includes more than onepushing screw, and the two or more pushing screws are turnedsimultaneously, alternately, or a combination thereof. In someembodiments, the cap-grabbing apparatus includes a first pushing screwand a second pushing screw, and the first ends of the first pushingscrew and the second pushing screw are turned simultaneously,alternately, or a combination thereof.

In some embodiments, the cap removed by the methods described herein isan NMR rotor cap. The NMR rotor cap, in some embodiments, has a diameterof about 3 mm to about 5 mm, about 3 mm to about 4 mm, or about 3.2 mm.Other sizes are envisioned, however, because the dimensions of a firstaperture and/or a plate, as described herein, can be altered toaccommodate a variety of sizes.

Microwave Waveguides

Also provided herein are microwave guides that are configured, in someembodiments, to steer a beam at a sample in a confined space within amagnetic resonance spectrometer.

Also provided herein are slotted waveguides. In some embodiments, theslotted waveguides include a metallic tube having a first end and asecond end, wherein the metallic tube defines a plurality of slots in asurface of the metallic tube, and wherein the first end of the metallictube is configured to be coupled to a device for directing orcontrolling electromagnetic radiation, such as microwaves. The slottedwaveguides may have a substantially smooth inner surface.

As used herein, the term “slot” refers to an aperture (i) defined by ametallic tube of a slotted waveguide, and (ii) having a length at least5 times, at least 10 times, at least 25 times, at least 50 times, or atleast 100 times greater than its width. The slots may be located at anyone or more portions of a surface of a slotted waveguide. In someembodiments, slots are present along the full length of a metallic tube,or along a portion of the metallic tube. The slotted waveguides,including the slots thereof, may be configured to allow the propagationof TE11 mode microwave beams with low losses.

The slots of a slotted waveguide may have uniform dimensions, or aplurality of slots may include slots having different dimensions. Theslots may be designed to be thin enough compared to the wavelength ofthe microwaves to not interfere with the beam propagation along thelargest dimension of the guide, and slots may be long enough to allowradio frequency waves to travel perpendicularly to the length of thewaveguide with limited losses.

In some embodiments, each slot of the plurality of slots has a widththat is about 4 to about 6 times smaller than a wavelength of amicrowave beam. In some embodiments, each slot of the plurality of slotshas a width that is about 5 times smaller than a wavelength of amicrowave beam. In some embodiments, each slot of the plurality of slotshas a width of about 120 μm to about 130 μm. In some embodiments, eachslot of the plurality of slots has a width of about 125 μm. The slotsgenerally may be dimensioned to be relatively long, such that the Eddycurrents are reduced or minimized (and thus reduce radio frequency (RF)losses while the RF waves travel through the slotted waveguide). Theslots also may be dimensioned to be very thin (e.g., about 5 timessmaller than the wavelength of the microwave), such that the microwavetraveling in the longitudinal direction do not “see” the slots.

In some embodiments, the slots are 125 μm wide, and the wavelength ofthe microwave is 760 μm, thus the slotted waveguide appears as if it isa solid cylinder to the microwave beam. This particular design canmaximize both the RF and microwave power at the sample. In order toprevent arcing from the RF wave (arcing between the NMR coil and theslotted waveguide) a tube of quartz, as described herein, may be placedaround the slotted guide to act as an insulator.

Each slot may be independently oriented at any angle relative to alongitudinal axis of a metallic tube. In some embodiments, each slot ofthe plurality of slots has a length that is oriented perpendicularly toa longitudinal axis of the metallic tube.

In some embodiments, the slotted waveguides provided herein also includea sample tube. The sample tube, in some embodiments, is configured to beinserted at least partially into the second end of the slottedwaveguide. The sample tube may be formed at least in part of adielectric material. For example, a sample tube may be formed entirelyof a dielectric material, or a portion of the sample tube, such as theportion inserted into a slotted waveguide, may be formed of a dielectricmaterial.

An embodiment of a slotted waveguide is depicted at FIG. 2 . The slottedwaveguide 200 of FIG. 2 is a metallic tube having a first end 210 and asecond end 220. The metallic tube defines a plurality of slots 230 inopposing surfaces of the metallic tube. A portion of the metallic tubeis enlarged to show the plurality of slots 230. The slotted waveguide200 of FIG. 2 includes 60 slots at or near the middle of the waveguide.When the slotted waveguide of FIG. 2 is used, a sample tube may becompletely inserted in the second end 220 of the metallic tube.

Another embodiment of a slotted waveguide is depicted at FIG. 3 . Theslotted waveguide 300 of FIG. 3 has a shorter length than the device ofFIG. 2 . The slotted waveguide 300 of FIG. 3 is a metallic tube having afirst end 310 and a second end 320. The metallic tube defines aplurality of slots 330 in a surface of the metallic tube. The slottedwaveguide 300 of FIG. 3 is 3.4 mm in diameter and about 20 mm long. Itslarger base at the first end 310 is 5 mm in diameter and includes abevel to self-center when assembled within a measurements probe. Theslots 330 in the slotted waveguide 300 are about ¾ around the peripheryof the metallic tube with an opening of 100 μm and a gap betweenopenings twice the opening width.

Also depicted at FIG. 3 is a sample tube 340, which is partiallyinserted into the second end 320 of the slotted waveguide 300. When theslotted waveguide depicted at FIG. 3 is used, about 1 mm to about 5 mmof the sample tube 340 may be inserted into the second end 320 of themetallic tube. The sample tube 340 of FIG. 3 has a diameter of about 3mm, and a length of about 30 mm, although other dimensions areenvisioned. In some embodiments, the sample tube 340 is formed of adielectric material, which is transparent to microwaves. Using atransparent dielectric sample tube allows, in some embodiments, amicrowave beam to propagate continuously from the metallic guide to thedielectric sample tube itself. This design can maintain the same lowloss microwave propagation as the device of FIG. 2 , but the radiofrequency irradiation can be performed from any angle. The device ofFIG. 2 can limit the radio frequency irradiation direction due to thespine needed to mechanically hold the metallic guide together. Withoutthe spine, radio frequencies can be directed at the sample from multipledirections at the same time without any losses. The device of FIG. 3 ,therefore, has a design that may offer new applications, such as thepossibility of performing two-dimensional NMR measurements due to tomulti-direction radio frequency irradiation without any interference. Insome embodiments, microwaves travel from the first end 310 through theslotted waveguide and into the sample tube 340, thereby allowingirradiation of the sample. The sample also can be irradiated with beamscoming from perpendicular directions to the propagation of the guidedmicrowaves.

Also provided herein are microwave guides that include a slottedwaveguide as described herein; a spline horn coupled to the first end ofthe slotted waveguide; and an elongated waveguide coupled the splinehorn.

In some embodiments, the elongated waveguide includes a tube having asubstantially smooth inner surface. In some embodiments, the elongatedwaveguide has an inner diameter of about 0.4 inches to about 0.5 inches.

In some embodiments, the elongated waveguide has an inner diameterconfigured to correspond to an incoming microwave beam generated by aseparate microwave source and a quasi-optical transport table.

The spline horn may be configured to focus a diameter of a beam ofelectromagnetic radiation from the elongated waveguide down to aninternal diameter of the slotted waveguide. In some embodiments, thespline horn includes a substantially smooth inner surface. The splinehorn may have a substantially smooth inner surface.

The spline shape of a spline horn may be modified to match the impedanceof an incoming microwave beam at the base of the probe (when theimpedance matches, the reflection of the beam is zero). In someembodiments, impedance matching is part of the design, and can make theentire waveguide lossless. The spline of the spine horn and theelongated waveguide may be shaped to turn the Gaussian shaped input beaminto a TE11 mode beam at its output. The TE11 mode microwave beam thencan continuously propagate into the slotted waveguide with minimallosses.

In some embodiments, the guides also include a tube of quartz arrangedat least partially around the slotted waveguide. A tube of quartz placedaround the slotted waveguide during NMR measurements can remove possibleelectrical grounding (i.e. generate electrical arcs) via the slottedwaveguide.

An embodiment of a microwave guide is depicted at FIG. 4 . The guide 400of FIG. 4 includes the slotted waveguide 200 of FIG. 2 , a spline horn410 coupled to the first end of the slotted waveguide 200; and anelongated waveguide 420 coupled the spline horn 410. The elongatedwaveguide 420 depicted at FIG. 4 has an inner diameter of 0.414 inches.The spline horn 410 includes a larger inner diameter at the end 411coupled to the elongated waveguide 420, and a smaller inner diameter atthe end 412 coupled to the slotted waveguide 200. This gradient may beconfigured to focus a diameter of a beam of electromagnetic radiationfrom the elongated waveguide down to an internal diameter of the slottedwaveguide. Although the slotted waveguide 200 of FIG. 2 is depicted inthe embodiment of FIG. 4 , the slotted waveguide 200 of FIG. 2 may bereplaced with the slotted waveguide 300 of FIG. 3 in other embodiments.The slotted waveguide 200 depicted at FIG. 4 had an inner diameter of0.118 inches.

In some embodiments, the microwave guide provided herein may include anadaptor configured to provide cooling to the sample. The adaptor, forexample, may be configured such that a cooling gas can be flown throughthe waveguide all the way to the sample. Although a portion of a gas mayflow out through the first few slots of a slotted waveguide, the gas maykeep flowing between a quartz tube and a slotted waveguide to cool thesample.

An embodiment of an adapter is depicted at FIG. 5A (top view) and FIG.5B (cross-sectional view). The adapter 500 includes a first end 510 anda second end 520 configured to accommodate components of the apparatusesprovided herein. The adapter 500 defines an orifice 530 through which agas may be provided.

An adapter also may include one or more windows arranged in or on theadapter. In some embodiments, the one or more windows are transparent(e.g., have a very low absorption) to microwaves in order to minimizereflections. For example, the thickness of a window may be about 1.5times the wavelength of the microwave). Such a material may be chosenfor its low index of refraction and its low loss to maximizetransmission. An adaptor also may serve, in some embodiments, as analignment pin to align the Gaussian microwave beam propagating towardthe NMR probe waveguide, thus ensuring perfect matching conditions (i.e.zero reflection losses) in some embodiments.

Also provided herein are analytical apparatuses that include the slottedwaveguides or other apparatuses, such as microwave guides, describedherein. In some embodiments, the microwave guide is arranged in an NMRprobe. In some embodiments, the microwave guide is arranged in a liquiddynamic nuclear polarization (DNP) probe.

For DNP applications, the microwave beam may interact with the sample(which may be placed in the center of the slotted waveguide) while atthe same time allowing RF waves to also interact with the sample.

In modern high-resolution NMR spectrometers, the RF waves are generatedby a radial (orientation relative to the NMR magnet) NMR saddle coilsituated around the sample (in some embodiments herein, around theslotted waveguide). The slots in the slotted waveguide may be designedto allow the RF waves to travel freely through the waveguide andinteract with the sample as if the slotted waveguide was transparent.

In some embodiments, the design/set-up increases the microwave beampower at the sample by several folds compared to the alternative method(e.g., use of a corrugated waveguide and launch of the beam toward thesample with the help of a lens). The apparatuses described herein, insome embodiments, are also simpler to manufacture than fabricatingcorrugated waveguide and horns for this application, thus reducing themanufacturing costs.

In the descriptions provided herein, the terms “includes,” “is,”“containing,” “having,” and “comprises” are used in an open-endedfashion, and thus should be interpreted to mean “including, but notlimited to.” When methods and devices are claimed or described in termsof “comprising” various components or steps, the devices and methods canalso “consist essentially of” or “consist of” the various components orsteps, unless stated otherwise.

The terms “a,” “an,” and “the” are intended to include pluralalternatives, e.g., at least one. For instance, the disclosure of “aplate,” “a tightening screw,” “a metal,” and the like, is meant toencompass one, or mixtures or combinations of more than one plate,tightening screw, metal, and the like, unless otherwise specified.

Various numerical ranges may be disclosed herein. When Applicantdiscloses or claims a range of any type, Applicant's intent is todisclose or claim individually each possible number that such a rangecould reasonably encompass, including end points of the range as well asany sub-ranges and combinations of sub-ranges encompassed therein,unless otherwise specified. Moreover, numerical end points of rangesdisclosed herein are approximate. As a representative example, Applicantdiscloses that, in some embodiments, each slot of the plurality of slotshas a width of about 120 μm to about 130 μm. This disclosure should beinterpreted as encompassing values of about 120 μm to about 130 μm, andfurther encompasses “about” each 121 μm, 122 μm, 123 μm, 124 μm, 125 μm,126 μm, 127 μm, 128 μm, and 129 μm, including any ranges and sub-rangesbetween any of these values.

The present embodiments are illustrated herein by referring to variousembodiments, which are not to be construed in any way as imposinglimitations upon the scope thereof. On the contrary, it is to beunderstood that resort may be had to various other aspects, embodiments,modifications, and equivalents thereof which, after reading thedescription herein, may suggest themselves to one of ordinary skill inthe art without departing from the spirit of the present embodiments orthe scope of the appended claims. Thus, other aspects of the embodimentswill be apparent to those skilled in the art from consideration of thespecification and practice of the embodiments disclosed herein.

We claim:
 1. A microwave guide comprising: a slotted waveguidecomprising a metallic tube having a first end and a second end, whereinthe metallic tube defines a plurality of slots in a surface of themetallic tube; a spline horn coupled to the first end of the slottedwaveguide; and an elongated waveguide coupled the spline horn, theelongated waveguide comprising a tube having a substantially smoothinner surface; wherein the spline horn is configured to focus a diameterof a beam of electromagnetic radiation from the elongated waveguide downto an internal diameter of the slotted waveguide.
 2. The microwave guideof claim 1, wherein the elongated waveguide has an inner diameter ofabout 0.4 inches to about 0.5 inches.
 3. The microwave guide of claim 1,wherein the elongated waveguide has an inner diameter configured tocorrespond to an incoming microwave beam generated by a separatemicrowave source and a quasi-optical transport table.
 4. The microwaveguide of claim 1, wherein the spline horn comprises a substantiallysmooth inner surface.
 5. The microwave guide of claim 1, furthercomprising a tube of quartz arranged at least partially around theslotted waveguide.
 6. The microwave guide of claim 1, further comprisinga sample tube formed at least in part of a dielectric material, whereinthe sample tube is inserted at least partially into the second end ofthe slotted waveguide.
 7. An analytical apparatus comprising themicrowave guide of claim
 1. 8. The analytical apparatus of claim 7,wherein the analytical apparatus comprises an NMR probe, wherein themicrowave guide is arranged in the NMR probe.
 9. A microwave guidecomprising: a slotted waveguide comprising a metallic tube having afirst end and a second end, wherein the metallic tube defines aplurality of slots in a surface of the metallic tube; a spline horncoupled to the first end of the slotted waveguide; an elongatedwaveguide coupled the spline horn, the elongated waveguide comprising atube having a substantially smooth inner surface; and a sample tubeformed at least in part of a dielectric material, wherein the sampletube is inserted at least partially into the second end of the slottedwaveguide; wherein the spline horn is configured to focus a diameter ofa beam of electromagnetic radiation from the elongated waveguide down toan internal diameter of the slotted waveguide.
 10. The microwave guideof claim 9, wherein the elongated waveguide has an inner diameter ofabout 0.4 inches to about 0.5 inches.
 11. The microwave guide of claim9, wherein the elongated waveguide has an inner diameter configured tocorrespond to an incoming microwave beam generated by a separatemicrowave source and a quasi-optical transport table.
 12. The microwaveguide of claim 9, wherein the spline horn comprises a substantiallysmooth inner surface.
 13. The microwave guide of claim 9, furthercomprising a tube of quartz arranged at least partially around theslotted waveguide.
 14. The microwave guide of claim 9, wherein each slotof the plurality of slots has a length that is oriented perpendicularlyto a longitudinal axis of the metallic tube.
 15. The microwave guide ofclaim 9, wherein each slot of the plurality of slots has a width that isabout 4 to about 6 times smaller than a wavelength of a microwave beam.16. The microwave guide of claim 9, wherein each slot of the pluralityof slots has a width of about 120 μm to about 130 μm.
 17. The microwaveguide of claim 9, wherein each slot of the plurality of slots has alength that is at least 5 times greater than its width.
 18. Themicrowave guide of claim 9, wherein each slot of the plurality of slotshas a length that is at least 50 times greater than its width.